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2.3 Objective-C and Objective-C++ languages

GCC supports “traditional” Objective-C (also known as “Objective-C 1.0”) and contains support for the Objective-C exception and synchronization syntax. It has also support for a number of “Objective-C 2.0” language extensions, including properties, fast enumeration (only for Objective-C), method attributes and the @optional and @required keywords in protocols. GCC supports Objective-C++ and features available in Objective-C are also available in Objective-C++.

GCC by default uses the GNU Objective-C runtime library, which is part of GCC and is not the same as the Apple/NeXT Objective-C runtime library used on Apple systems. There are a number of differences documented in this manual. The options ‘-fgnu-runtime’ and ‘-fnext-runtime’ allow you to switch between producing output that works with the GNU Objective-C runtime library and output that works with the Apple/NeXT Objective-C runtime library.

There is no formal written standard for Objective-C or Objective-C++. The authoritative manual on traditional Objective-C (1.0) is “Object-Oriented Programming and the Objective-C Language”, available at a number of web sites:

The Objective-C exception and synchronization syntax (that is, the keywords @try, @throw, @catch, @finally and @synchronized) is supported by GCC and is enabled with the option ‘-fobjc-exceptions’. The syntax is briefly documented in this manual and in the Objective-C 2.0 manuals from Apple.

The Objective-C 2.0 language extensions and features are automatically enabled; they include properties (via the @property, @synthesize and @dynamic keywords), fast enumeration (not available in Objective-C++), attributes for methods (such as deprecated, noreturn, sentinel, format), the unused attribute for method arguments, the @package keyword for instance variables and the @optional and @required keywords in protocols. You can disable all these Objective-C 2.0 language extensions with the option ‘-fobjc-std=objc1’, which causes the compiler to recognize the same Objective-C language syntax recognized by GCC 4.0, and to produce an error if one of the new features is used.

GCC has currently no support for non-fragile instance variables.

The authoritative manual on Objective-C 2.0 is available from Apple:

For more information concerning the history of Objective-C that is available online, see http://gcc.gnu.org/readings.html


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